Process to form an adhesion layer and multiphase ultra-low k dielectric material using PECVD
A first PECVD process incorporating a silicon oxide precursor alone and then with an organo-silicon precursor with increasing flow while the flow of the silicon oxide precursor is reduced to zero provides a graded carbon adhesion layer whereby the content of C increases with layer thickness and a second PECVD process incorporating an organo-silicon precursor including an organic porogen provides a multiphase ultra-low k dielectric. The multiphase ultra-low k PECVD process uses high frequency radio frequency power just above plasma initiation in a PECVD chamber. An energy post treatment is also provided. A porous SiCOH dielectric material having a k less than 2.7 and a modulus of elasticity greater than 7 GPa is formed.
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The present invention relates to a process to form multiphase ultra low k dielectric material and more particularly to a plasma enhanced chemical vapor deposition (PECVD) process to form porous SiCOH and to a dielectric material having a k lower than 2.7 and a modulus of elasticity greater than 7 GPa.
BRIEF SUMMARY OF THE INVENTIONIn accordance with the present invention, a method for forming an ultra low k dielectric layer comprising selecting a plasma enhanced chemical vapor deposition chamber; placing a substrate in the chamber; introducing an organo-silicon precursor including an organic porogen into the chamber; heating the substrate to a temperature in the range from 200° C. to 350° C.; controlling the amount of an oxidant gas in the chamber; forming a deposited layer by applying a high frequency radio frequency power in the chamber to initiate a plasma and polymerization of the organo-silicon precursor and retain at least a fraction of the organic porogen in the deposited layer; after a period of time terminating the plasma in the chamber; and applying to the deposited layer an energy post treatment selected from the group consisting of thermal anneal, ultra violet (UV) radiation, and electron beam irradiation to drive out the organic porogen and increase the porosity in the deposited layer to at least five percent.
The invention further provides a porous SiCOH dielectric material having a tri-dimensional random covalently bond network of Si—O, Si—C, Si—CH2—Si, C—O, Si—H and C—H bonds, a dielectric constant k lower than 2.7 and a modulus of elasticity greater than 7 GPa.
The invention further provides a semiconductor integrated circuit comprising interconnect wiring having a porous SiCOH dielectric material having a tri-dimensional random covalently bond network having a dielectric constant k lower than 2.7 and a modulus of elasticity greater than 7 GPa.
The invention further provides a semiconductor integrated circuit comprising a FET having a gate stack spacer including a porous SiCOH dielectric material having a tri-dimensional random covalently bond network having a dielectric constant k lower than 2.7 and a modulus of elasticity greater than 7 GPa.
These and other features, objects, and advantages of the present invention will become apparent upon consideration of the following detailed description of the invention when read in conjunction with the drawing in which:
Referring now to the drawing,
Dielectric layer 18 may be formed in a PECVD chamber by placing a substrate in the chamber and introducing an organo-silicon precursor including an organic porogen into the chamber. The organo-silicon precursor introduced may be a single organo-silicon precursor. An organo-silicon precursor may be selected from the group consisting of octamethylcyclotetrasiloxane (OMCTS) and 1,3,5,7-tetraoctamethylcyclotetrasiloxane (TMCTS), diethoxymethylsilane (DEMS), diethyldimethoxysilane (DMDMOS, diethyldimethoxysilane (DEDMOS), other cyclic and non-cyclic silanes, and other cyclic and non-cyclic siloxanes. The pressure in the chamber is controlled to be in the range from 5 to 9 Torr. and preferably about 7 Torr. Substrate 12 may be heated to a temperature in the range from 200° C. to 350° C. and preferably heating only in the range from 200° C. to 250° C. The flow of an oxidant gas into the chamber is controlled and may be reduced to zero after graded dielectric layer 16 is formed and prior to forming dielectric layer 18. The oxidant gas may be selected from the group consisting of O2, H2O, CH3OH, and C4H10O. Other gas that may be introduced into the chamber may be inert Ar, a reactive oxygenated gas and an oxygenated hydrocarbon gas. Dielectric layer 18 may have a tri-dimensional random covalently bond network of Si—O, Si—C, Si—CH2—Si, C—O, Si—H and C—H bonds, a dielectric constant k lower than 2.7 and a modulus of elasticity greater than 7 GPa or a dielectric constant k lower than 2.6 and a modulus of elasticity greater than 6 GPa. The modulus of elasticity in dielectric layer 18 is uniform in all directions or isotropic.
Dielectric layer 18 may be formed by applying high frequency radio frequency power in the PECVD chamber just above the plasma initiation power level. The high frequency power may be at or greater than 400 kHz and the radio frequency power may be at or greater than 13.56 MHz. The power just above the plasma initiation power level is typically a power increase above plasma initiation in the range from 75 to 800 watts for a 300 mm radius substrate in a Plasma CVD chamber and preferable in the range from 150 to 450 watts for a 300 mm radius substrate in a Plasma CVD chamber to maintain a stable plasma at minimum power. By setting the high frequency radio frequency power just above plasma initiation, an increase in polymerization occurs and an increase in retention of an organic porogen in the deposited dielectric layer occurs. Further, minimum plasma dissociation of an organic functional group occurs in the plasma and cross-linking of large molecules occur to form a deposited dielectric layer with a high degree of porosity in the range from 5 to 16.5 percent after an energy post treatment.
The growth of dielectric layer 18 is stopped or terminated by lowering the high frequency radio frequency power in the PECVD chamber until the plasma terminates. The as-deposited dielectric layer 18 may have a dielectric constant in the range from 2.63 to 2.65, a porosity in the range from 5.5 to 8.5 percent, a pore diameter in the range from 1 to 1.2 nm, a modulus of elasticity in the range from 1.18 to 6.3 GPa, a hardness in the range from 0.28 to 0.59, a carbon content in the range from 37.7 to 32.5 atomic percent, an oxygen content in the range from 29.6 to 32.4 atomic percent, a silicon content in the range from 32.8 to 34.9 atomic percent, a stress in the range from 19 to 40 MPa and a ratio of stress/modulus of elasticity in the range from 16.1 to 15.5. The organo-silicon precursor for the dielectric layer measured to obtain the above data was octamethylcyclotetrasiloxane (OMCTS) with the optional addition of an oxygen oxidant source (i.e. O2/N2O). The measurements were made from dielectric layers made at substrate temperatures of 250° C., 280° C., 300° C. and 350° C.
The as-deposited dielectric layer 18 may be subjected to an energy post treatment of ultra violet radiation for a time period of 300 sec at a dielectric layer temperature above 200° C. to increase Si—CH2—Si cross linking bonds in dielectric layer 18. Dielectric layer 18 typically has two adjacent Si—CH3+Si—CH3 chemical bonds in the deposited dielectric layer which change to Si—CH2—Si bonds to increase the modulus of elasticity and hardness of dielectric layer 18 and outgas of volatile CH4 to create additional pores in deposited dielectric layer 18. The energy post treatment thermal anneal may include heating the as-deposited dielectric layer 18 to a temperature in the range from 200° C. to 430° C. in an ambient of forming gas (H2 and N2) for a period of time greater than 40 minutes.
The as-deposited dielectric layer 18 characteristics for the dielectric layer described above change after an energy post treatment of ultra violet radiation for a time period of 300 sec at a temperature above 200° C. The wavelength of UV may be a narrow spectrum or a broad spectrum. Certain wavelengths of UV enhance specific reactions. Dielectric layer 18 after the energy post treatment has a dielectric constant in the range from 2.39 to 2.60, a porosity in the range from 13.8 to 16.6 percent, a pore diameter in the range from 0.8 to 1.0 nm, a modulus of elasticity in the range from 4.92 to 13.83 GPa, a hardness in the range from 1.27 to 1.75, a carbon content in the range from 31.3 to 32.3 atomic percent, an oxygen content in the range from 33.7 to 34.4 atomic percent, a silicon content in the range from 34.4 to 35.2 atomic percent, a stress in the range from 73 to 110 MPa and a ratio of stress/modulus of elasticity in the range from 6.8 to 16.9.
Other energy post treatment besides UV radiation may be thermal anneal and electron beam (EB) irradiation. Thermal anneal treatment is especially applicable where dielectric layer 18 is vertical such as if used as a gate stack sidewall spacer on a field effect transistor or if portions of the layer are vertical and other portions are horizontal. UV radiation and EB irradiation may provide an uneven exposure to a vertical dielectric layer. Energy post treatment functions to drive out the organic porogen and to increase the porosity in the deposited dielectric layer 18. Dielectric layer 18 may have a dielectric constant lower than 2.7 and a modulus of elasticity greater than 7 GPa or greater than 8 GPa or a dielectric constant lower than 2.5 and a modulus of elasticity greater than 6 GPa.
The marked absorption peak 57 at 1359 cm−1 of Si—CH2—Si is shown with an absorbance of 0.0075.
In
In
A second interconnect level comprises graded dielectric layer 106, vias 108 and 110, dielectric layer 112, metal wiring 114 and 115 and dielectric cap layer 118. Graded dielectric layer 106 functions to provide adhesion to upper surface 104 of dielectric cap layer 99. Dielectric cap layer 99 functions to provide a diffusion barrier to metal from the upper surface of metal wiring 94 and 95.
A third interconnect level comprises graded dielectric layer 126, via 128, dielectric layer 132 and metal wiring 134 and 135. Graded dielectric layer 126 functions to provide adhesion to upper surface 124 of dielectric cap layer 118.
In
While there has been described and illustrated a method for forming an ultra low k dielectric layer and a dielectric with k below 2.7 and a modulus of elasticity greater than 7 GPa, it will be apparent to those skilled in the art that modifications and variations are possible without deviating from the broad scope of the invention which shall be limited solely by the scope of the claims appended hereto.
Claims
1. A method for forming an ultra low k dielectric layer comprising:
- selecting a plasma enhanced chemical vapor deposition chamber;
- placing a substrate in said chamber;
- introducing a first organo-silicon precursor including an organic porogen into said chamber;
- heating said substrate to a temperature in the range from 200° C. to 350° C.;
- controlling the amount of an oxidant gas in said chamber;
- forming a deposited layer by applying high frequency radio frequency power in said chamber to initiate a plasma and polymerization of said first organo-silicon precursor and retain at least a fraction of said organic porogen in said deposited layer;
- after a period of time terminating said plasma in said chamber; and
- applying to said deposited layer an energy post treatment selected from the group consisting of thermal anneal, ultra violet (UV) radiation, and electron beam irradiation to drive out said organic porogen and increase the porosity in said deposited layer to at least five percent;
- wherein prior to introducing said first organo-silicon precursor introducing a flow of a silicon oxide precursor alone followed by introducing an increasing flow of a second organo-silicon precursor while reducing said flow of said silicon oxide precursor to form a graded layer where the content of C increases with thickness.
2. The method of claim 1 wherein said applying an energy post treatment includes heating to a temperature above 200° C. for a time period to increase Si—CH2—Si cross linking bonds in said deposited layer.
3. The method of claim 1 wherein said applying an energy post treatment includes heating to a temperature above 200° C. for a time period to cause adjacent Si—CH3 chemical bonds in said deposited layer to change to Si—CH2—Si bonds to increase a modulus of elasticity and hardness of said deposited layer.
4. The method of claim 1 wherein said first organo-silicon precursor is selected from the group consisting of octamethylcyclotetrasiloxane (OMCTS) and 1,3,5,7,-tetraoctamethylcyclotetrasiloxane (TMCTS), diethoxymethylsilane (DEMS), dimethyldimethoxysilane (DMDMOS, diethyldimethoxysilane (DEDMOS), other cyclic and non-cyclic silanes, and other cyclic and non-cyclic siloxanes.
5. The method of claim 1 further including controlling a pressure in said chamber in the range from 5 to 9 Torr.
6. The method of claim 1 wherein applying high frequency radio frequency power includes applying high frequency radio frequency power just above plasma initiation to increase polymerization whereby little plasma dissociation of an organic functional group occurs in said plasma in said chamber.
7. The method of claim 1 wherein applying high frequency radio frequency power includes a power increase above plasma initiation in the range from 75 to 800 watts.
8. The method of claim 1 wherein said heating said substrate includes heating only in a temperature range from 200° C. to 250° C.
9. The method of claim 1 wherein said energy post treatment includes a thermal anneal of heating said deposited layer in the range from 200° C. to 430° C. in an ambient selected from the group consisting of an inert gas and forming gas and for a period of time greater than 40minutes.
10. The method of claim 1 further including introducing a gas selected from the group consisting of inert Ar, reactive oxidant gas, and oxygenated hydrocarbon gas in said chamber.
11. The method of claim 1 wherein said oxidant gas is selected from the group consisting of O2, H2O, CH3OH, and C4H10O.
12. The method of claim 1 wherein said dielectric layer has a dielectric constant k lower than 2.7 and a modulus of elasticity greater than 7 GPa.
13. The method of claim 1 wherein said dielectric layer has a dielectric constant k lower than 2.5 and a modulus of elasticity greater than 6 GPa.
14. The method of claim 1, wherein said content of C increases with thickness to above 30 percent.
15. The method of claim 1 wherein said introducing a silicon oxide precursor is terminated at times when said graded layer thickness is in the range from 3 nm to 7nm.
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Type: Grant
Filed: Aug 19, 2011
Date of Patent: Jan 28, 2014
Patent Publication Number: 20130043514
Assignee: International Business Machines Corporation (Armonk, NY)
Inventors: Alfred Grill (White Plains, NY), Thomas Jasper Haigh, Jr. (Claverack, NY), Kelly Malone (Newburgh, NY), Son Van Nguyen (Schenectady, NY), Vishnubhai Vitthalbhai Patel (Yorktown Heights, NY), Hosadurga Shobha (Niskayuna, NY)
Primary Examiner: Stephen W Smoot
Assistant Examiner: Vicki B Booker
Application Number: 13/214,157
International Classification: H01L 21/31 (20060101); H01L 21/469 (20060101);